Hydroxylamines and salts thereof are being used in industry over a wide range of uses such as raw material of intermediate for medicines or agrochemicals, surface-treating agent for metal, fiber treatment or dyeing. Free hydroxylamines have a very unstable property, for example, these readily undergo decomposition in the presence of metal ion (particularly, heavy metal ion) under the high-temperature or high-concentration condition. Accordingly, in general, a salt of hydroxylamine, which is relatively stable, is produced and used.
However, in many uses, a hydroxylamine is more preferred than a salt of hydroxylamine and also, an aqueous hydroxylamine solution in a high concentration is often required. Furthermore, for use in electronic industry, a high-purity hydroxylamine having less metal impurities is required. In order to meet these requirements, attempts are being made to suppress the decomposition reaction and efficiently and safely produce a high-concentration aqueous hydroxylamine solution.
For example, German Patent Publication No. 3,528,463 (Patent Document 1) discloses a process of adding an oxide and/or a hydroxide of calcium, strontium or barium to an aqueous hydroxylamine sulfate solution having a small ammonium ion content, performing the reaction at a temperature of 20° C. or less and removing by separation the insoluble sulfate.
JP-A-2002-12415 (Patent Document 2) discloses a process of producing a hydroxylamine by adding a slurry of calcium oxide and/or calcium hydroxide to an aqueous solution containing hydroxylamine sulfate, thereby performing the reaction, where the reaction is performed in the state that calcium sulfate as the seed slurry is always present in the reaction system, as a result, the particle size of insoluble sulfate is increased to enhance the filtration efficiency and a hydroxylamine is efficiently produced.
However, these conventional processes of adding an alkali compound to an aqueous solution containing hydroxylamine sulfate have a problem that the produced hydroxylamine forms a complex with a sulfate produced as a by-product or adsorbs to the sulfate and the yield of hydroxylamine decreases.
Also, JP-A-2000-510385 (Patent Document 3) describes a process of separating an aqueous solution containing a hydroxylamine and a salt into an aqueous hydroxylamine solution and a salt fraction by stripping.
JP-A-2001-513479 (Patent Document 4) describes a process of treating a salt of hydroxylamine with a base and separating the produced solution into an aqueous hydroxylamine solution and a salt fraction.
JP-A-2002-504062 (Patent Document 5) describes a process of concentrating an aqueous hydroxylamine solution by distillation, removing the hydroxylamine-containing vapor from the side face at the column bottom, and concentrating the vapor.
U.S. Pat. No. 6,235,162 (Patent Document 6) describes a process of obtaining a hydroxylamine by extracting a hydroxylamine from the column top by distillation and further distilling the obtained distillate.
JP-A-2002-68718 (Patent Document 7) describes a process of distilling out a hydroxylamine from the column top by simply distilling an aqueous hydroxylamine solution.
However, these processes have a problem that at the time of obtaining a hydroxylamine from the column top or side by distillation, the hydroxylamine may undergo decomposition or explosion due to distillation at a high temperature.
[Patent Document 1]German Patent Publication No. 3,528,463[Patent Document 2]JP-A-2002-12415[Patent Document 3]JP-A-2000-510385[Patent Document 4]JP-A-2001-513479[Patent Document 5]JP-A-2002-504062[Patent Document 6]U.S. Pat. No. 6,235,162[Patent Document 7]JP-A-2002-68718